I propose that the patches be put onto the Gentoo Mirrors and stored in a new
directory called "patchfiles" which could be placed beside "distfiles".

It would be advantageous to have a list of available patches within the portage
tree so that it can be updated during "emerge sync". A file named "dtu.list"
can be created and placed in $PORTDIR/profiles.

If a machine can be set up to generate patches it should contain a local mirror
of distfiles which it can monitor for added packages. When a package is added
to distfiles the machine can try to determine the previous tarball so a patch
can be made and placed in the patchfiles dir. In addition, special-case patches
can be added manually.

The dtu.list file will be maintained by a special script. Whenever patches
are added or removed to the patchfiles dir, the script will make necessary
additions/removals in dtu.list. This will be done with minimal changes in the
file so it can be synchronized efficiently.

The system will be optional for users and can be enabled by making portage
invoke efetch through the FETCHCOMMAND environment variable [3].

When a package fetch is requested, the efetch/fetchcommand scripts (part of
Deltup) will scan the dtu.list file for updates and try downloading and applying
them if they exist, or fall back to a full package download if they don't or if
the patching process fails.

The most controversial feature has been the addition of dtu.list to the portage
tree, so in this section I will list the reasons I support it.

Flexibility. Without it, there must be a standard naming scheme which we
would be stuck with once the system is in place. Changing the system would
require serious compatibility breaks. With the dtu.list file we can change
the naming scheme easily without problems, or even have several different
naming schemes.

Features. Without patch information detecting different upgrade paths would
be impossible. Split package patching would also be impossible. If the info
is available we can use it to find the quickest upgrade path, like jumping
from a .0 release, or even disable certain patches if there are problems with
them.

It would be impossible to know which packages to upgrade from in some cases,
including renamed packages.

Knowing which patches are available will eliminate the overhead of attempting
to download patches which don't exist.

The dtu.list file will contain several hundred kilobytes of data. That has
caused some concern over how efficiently it can be rsynced. To address these
concerns the file's format will be plaintext and care has been taken to
minimize the number of changes as removals/additions are made.